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Inside Einstein's Mind | General Relativity Today

Watch a team of physicists try to prove one of Albert Einstein’s predictions of general relativity—that heavy objects distort time—in this video from NOVA: Inside Einstein’s Mind. Einstein’s theory holds that time speeds up as we travel away from the mass of a planet and gravity weakens. To test this, the physicists place two atomic clocks at different elevations on Earth. After four days, the difference between the clocks' ticks is slight but measurable. Using the Global Positioning System (GPS) as an example, the video also explains how time distortion can impact our daily lives.

After watching the videos, students will answer respective questions on the “Exploring Einstein’s Thought Experiments” worksheet. Groups assigned to watching “Einstein’s Special Theory of Relativity” will answer Part A, and groups assigned to watching “Gravity Is Acceleration” will answer Part B.

Emphasize to students that every member of their group should be able to explain the thought experiment and understand its importance to physics. When groups have finished answering their questions, pair the Part A groups with the Part B groups. Each group should explain its thought experiment. Then, groups should fill out the other part of the worksheet that they have not yet completed. Encourage discussion among groups rather than copying information down.

When finished, all groups should watch “General Relativity Today” and complete Part C. The class should then discuss the significance of Einstein’s findings on technology today and answer the following questions as a class:

What made Einstein so famous?

How have his theories shaped the way that we view the world?

If there is time, have students present their ideas for testing Einstein’s theories to the class and have the class provide constructive criticism to the groups.

Within two years of publishing his special theory of relativity in 1905, Albert Einstein already knew its limits. The theory found a way to resolve an inconsistency between classical mechanics and electromagnetism. But it was not compatible with Isaac Newton's law of universal gravitation. Einstein, like Newton before him, could not explain how gravity exerts its influence throughout the universe.

The problem was especially tricky because gravity treats all objects, without exception, in the same way. Einstein did not know how to approach it. However, one day, he experienced what he would later call the happiest thought of his life: that a free-falling man cannot sense his own weight. From this idea, Einstein established that gravity and acceleration not only felt the same, they were the same. This realization would serve as the foundation of his general theory of relativity, published in 1915. This revolutionary new theory at last reconciled relativity and gravitation.

Scientists who came before Einstein provided a foundation for his theories. But Einstein approached the information in a different way. He had a knack for reducing hard physical problems to concise yet convincing mental concepts. He called these mental concepts thought experiments. A thought experiment is a way to test a scenario for which an actual experiment is not practical. Einstein tried to understand gravity in terms of the geometry of space and time. Through his thought experiments, he developed a new description of gravity. It was not a force, as classical Newtonian physics explained. Rather, it was a curvature in the fabric of space and time due to the mass of objects.

The theories that arise from thought experiments may later be proven or disproven by experimental physics. In Einstein’s day, the technology didn’t exist to test many of the predictions of this theory. Today, technology is catching up to the science. For example, the invention of a highly precise atomic clock, accurate to within a second over billions of years, has enabled scientists to test one of Einstein's predictions. Einstein thought that time slows down or speeds up depending on the position and speed of an observer. This phenomenon is called time dilation. In a 2010 experiment, atomic clocks showed that time moves faster the higher you are in elevation, just as Einstein predicted. How much faster? A person would age about one-tenth of a microsecond faster over a lifetime for every foot he or she lived above ground level.

Here are suggested ways to engage students with this video and with activities related to this topic.

Before watching

Ask students:

What is Einstein’s general theory of relativity?

While watching

Pause the video at 1:30 and have students address the following:

According to Einstein’s general theory of relativity, what should we expect to see with the two clocks? Make a prediction as to what the scientists will see when they compare the clock that was on the mountain with the clock that was at sea level.

After watching

Ask students:

How does the Global Positioning System (GPS) take into account effects predicted by general relativity to pinpoint location?